Internal-combustion engine of compound type



APPLICATION FILED MAR. 81 l9l8.

Patented Apr. 13, 1920.

2 SHEETS-SHEET I.

6 Ci'usfaa S. G. WlGELlUS AND N. W. UHR. INTERNAL COMBUSTION ENGINE 0FCOMPOUND TYPE.

APPLICATION FILED MAR. 3. 1918.

Patented Apr. 13, 1920.

2 SHEETS-SHEET 2.

UNITED sTATES PATENT OFFICE.

SVEN GUS'I'AF WIGELIUS AND NILS WILHELM UHR, 0F GOT'IENBORG, SWEDEN.

INTERNAL-COMBUSTION ENGINE 0F COMPOUND TYPE.

Specification of Letters Patent.

Patented Apr. 13, 1920.

Application filed March 8, 1918. Serial No. 221,217.

To all whom it may concern:

Be it known that we, SVEN GUs'rAr WIGELIUS and NILs VVILHELM UHR,subjects of the King of Sweden, residing at Gottenborg, Sweden, haveinvented certain new and useful Improvements in Internal-CombustionEngines of Compound Type, of which the following is a specification.

The present invention refers to an arrangement in internal combustionengines of compound type in .which the cylinders are placed incommunication with each other after the high pressure piston has movedthrough a part of its stroke, and in which the high pressure cylinder isscavenged during expansion in the low pressure cylinder. 7

The invention relates more particularly to compound engines of the typeabovementioned, in which the high pressure piston also controls theexhaust from the low pressure cylinder, so as to cause an afterexpansionto take place in the low pressure cylinder when the connection betweenthe cylinders is closed on the return stroke of the high pressurepiston. The purpose of the invention is to bring about an effectivescavenging of the high pressure cylinder after every charge, and toavoid losses thatmight otherwise be caused by a vacuum arising in thelow pressure cylinder. To this end, accordingto this invention, thescavenging is carried on with an excess pressure sufficient to prevent avacuum from being, produced during the after-expansion in the lowpressure cylinder.

Another object of the invention is to make the expansion in thecylinders inclependent of the variations of the charge, so that the sameend pressure, above atmospheric, is always obtained in the low pressurecylinder. For this purpose the time of opening of the fresh air valve ismade dependent on the variations of the charge, so that the scavengingalways takes place at an excess pressure sufiicient to prevent a vacuumto be produced during the afterexpansion. Preferably the scavenging iscarried on at an excess pressure of 0.5 to 1 atmosphere, while theexhaust takes place at a slight excess pressure of 0.2 to 0.3atmosphere.

' In the specification the expression variation of the charge means theVariations of the amount of fuel introduced into the high pressurecylinder for each power stroke.

The variation of the charge differs according as the invention isapplied to an englne working according to the explosion method or to anengine of the Diesel type. In the former case the charge is varied byvarying the proportion between the fuel and the air in the fuel mixture,and in the latter case the charge is varied by varying the length oftime during which the injec tion takes place. In the case of Dieselengines different charges may be designated as in steam engines by thefilling, 2'. 6., the ratio between the length of the stroke dur ingwhich injection takes place, and the whole length of the stroke. Thus afilling of 20% designates a charge corresponding to the injection beingcarried on over 20% of the stroke of the piston.

The invention will be more fully described with reference to the drawingas applied to internal combustion engines of the Diesel type.

Figure 1 is an indicator diagram of a compound engine of this character.

Fig. 2 is a fragmentary section through the two engine cylinders showingthe high pressure piston in its uppermost position.

Fig. 3 is a similar section, the high pressure piston being shown at theinstant at which it opens the port between the two cylinders, and theangular relation of the cranks for the pistons being indicated.

Fig. i shows the high pressure piston at its lowermost position in asection similar to that in Fig. 2.

Fig. 5 is a similar section illustrating the high pressure piston at thepoint where it begins to clos the communicating port, and showing thefresh air valve open for admission of scavenging air to both cylinders.

Fig. 6 is a similar section showing the high pressure piston at thepoint where it has closed the communicating port, and where the freshair valve for admission of scavenging air is again'returned to closingposition.

1 is the high pressure cylinder, 2 the high pressure piston, 3 the lowpressure cylinder and 4' low pressure piston, 5 is the exhaust channeland 6 an annular recess in the piston 2 for blowing out from the lowpressure cylinder chamber through the port 7 in the wall between the twocylinders.

8 is the fueland air inlet valve and 9 the air valve for scavenging thehigh pres sure cylinder.

Under the low pressure piston & there is an air inlet valve 10 to, andan air outlet valve 11 from, the chamber 12 under the piston. By meansof the channel 13 the chamber 12 is in communication with the chamber14: above the valve 9.

The method of working is as follows Fig. 2 shows the parts in theposition which they occupy at the beginning of the charging operationand of the combustion. The piston 2 now moves downward, but the piston4, on the other hand, upward, blowing out taking place at the same timefrom the low pressure cylinder chamber through the recess 6 and theexhaust channel 5. When the piston 2 has completely covered the port 7,the piston 1 is in such a position that its upper edge has reached aboutthe lower edge of the port 7, and compression begins in the low pressurecylinder. In consequence of the angular crank-position, which, suitably,is about 110 (between 90 and 180) the piston 2 now runs with greatspeed, and the piston 4, on the other hand, at low speed.

Approximately when the upper edge of the piston 2 has passed the upperedge of the port 7, the two cylinders are placed in communication witheach other, and the low pressure piston begins its return stroke atabout the same instant. The pressure at that instant is about the samein both cylinders. Both the pistons now move downward, and expansiongoes on in both cylinder chambers.

When the high pressure piston 2 begins its return stroke, the lowpressure piston 4: has not yet reached the end of its stroke, but hasjust gone beyond the middle of its stroke. During the followingmovement, therefore, the expansion is continued as, firstly, the lowpressure piston is considerably larger than the high pressure piston,and, as, secondly, the low pressure piston moves at this time withconsiderably greater speed than the high pressure piston, for whichreason the increase of volume in the low pressure cylinder is many timesgreater than the volume diminution in the high pressure cylinder pertime unit.

During the downward movement of the low pressure piston 4, the air whichhas been drawn inby suction in through the valve 10 during the up-strokeis compressed in the chamber 12, the channel 13 and the chamber 14, andwhen the pressure on. the air amounts to about 1.5 atmosphere, thepressure in the two cylinder chambers has, at the same time, fallen tothe same, or a somewhat lower value, for which reason the valve 9 opensautomatically. The low pres sure piston still moves downward, and thescavenging of the high pressure chamber continues during the downwardmovement of the piston 4.

During the scavenging period the opening of the channel 5 is kept closedby the solid portion of the piston 2, so that, during the whole of thescavenging period the low pressure cylinder chamber is cut oil from thechannel 5. At no instant is the high pressure cylinder chamber stand indirect communication with channel 5.

During the continued up-stroke of the high pressure piston 2, the port 7is first covered by that piston, and then a further expansion, that is,an after-expansion, takes place in the low pressure cylinder, while thelow pressure piston is still moving downwardly. At the same time thecompression of the fresh air previously introduced into the highpressure cylinder chamber goes on until the piston 2 has reached itshighest point, when the fuel injection and combustion begin.

As soon as the port 7 has come into communication with the recess 6 and,consequently, with the exhaust channel 5, which has taken place duringthe latter part of the up-stroke of the piston 2, and as soon as thepiston f has started on its return stroke, the blowing out operationbegins from the low pressure cylinder chamber, and it continues evenafter the piston 2 has begun its return stroke. The continued method ofworking has been described above.

The pressure conditions of the two cylinders appear from Fig. 1, whichshows the pressure curve of the high pressure cylinder designated bysmall letters and the pressure curve of the low pressure cylinderdesignated by capitals. Fuel injection takes place along the line (0-6,the length of which represents the degree of admission. At '0 and Crespectively the two cylinders are put in communication with each other.C-D represents the simultaneous expansion in both cylinders. At D thescavenging begins. DE represents the scavenging and EF theafter-expansion.

Normally, i. e.'at a degree of admission of 20%, the expansion in thelow pressure cylinder is carried down to a pressure of 1.5 or 2atmospheres, and this pressure is reached at the point D, wherescavenging begins. During the after-expansion D--E the pressure islowered to about 1.2 or 1.3 atmospheres. If now the degree of admissionis changed to say 15%, as indicated by ab, the expansion would followthe clotted line bc and a pressure of 1.5 atmospheres would be reachedalready at the point D." This would result in a vacuum being producedduring the following expansion were it not for the fact that accordingto the invention the fresh air valve is opened at an earlier moment whenthe degree 'of admission is reduced. Thus in this alternative casethefresh air valve is openedatthe point D'. I I .7

We claim:

1. In an internal combustion compound engine of the type wherein a highpressure cylinder is in communication with a low pressure cylinder, andwherein the high pressure piston controls the communication between saidcylinders so as to cause an after-expansion in the low pressure cylinderupon closing this communication, means for introducing scavenging air tothe cylinders at an excess pressure suflicient to prevent the creationof a vacuum during said afterexpansion, the relation between the highpressure piston and low pressure piston being such that the highpressure piston closes the communication to the low pressure pistonafter the scavenging operation is finished.

2. In an internal combustion compound engine of the type wherein a highpressure cylinder is in communication with a low pressure cylinder, thehigh pressure piston controlling the connection between said cylindersso as to cause an after-expansion in the low pressure cylinder 011closing the connection between the cylinders, means for introducingscavenging air to the cylinders at an excess pressure sufficient toprevent the creation of a vacuum during said afterexpansion, and meansfor automatically varying the supply of fresh air in accordance with thevariations of the charge, the relation of the high pressure'piston tothe low pressure piston being such that the com- 'munication between thetwo cylinders is closed by the high pressure piston after the scavengingoperation is finished.

3. In an internal combustion compound engine of the type wherein a highpressure cylinder is in communication with a low pressure cylinder, thehigh pressure piston controlling the connection between said cylindersso as to cause an after-expansion in the low pressure cylinder onclosing the connection between the cylinders, means for introducingscavenging air to the cylinders at an excess pressure to prevent thecreation of a vacuum during said after-expansion, and apressure-controlled fresh air valve on the high pressure cylinder, therelation of the high pressure piston to the low pressure piston beingsuch that the communication between the cylinders is closed after thescavengin operation is finished.

4. 11 an internal combustion compound engine of the type wherein a highpressure cylinder is in communication with a low pressure cylinder, thehigh pressure piston controlling the connection between said cylindersso as to cause an after-expansion in the low pressure cylinder onclosing the connection between the cylinders, means for introducingscavenging air to the cylinders at an excess pressure suificient toprevent the creation of a vacuum during said after-expansion, a pressurecontrolled valve on the high pressure cylinder, and a passage-wayleading from said valve to an air outlet port in the suction chamber ofthe low pressure piston.

5. In an internal combustion compound engine of the type wherein a highpressure cylinder is in communication with a low pressure cylinder, thehigh pressure piston controlling the connection between said cylindersso as to cause an after-expansion in the low pressure cylinder onclosing the connection between the cylinders after the scavengingoperation is finished, means for introducing scavenging air to thecylinders at an excess pressure sufiicient to prevent the creation of avacuum during said after-expansion, a passage connecting the outercompartment of the low pressure cylinder with the high pressurecylinder, and a pressurecontrolled fresh air valve provided in saidpassage and adapted to open only after the high pressure piston hasturned and begun its return stroke.

6. In an internal combustion compound engine of the type wherein a highpressure cylinder is in communication with a low pressure cylinder, thehigh pressure piston controlling the connection between said cylindersso as to cause an after-expansion in the low pressure on closing theconnection between the cylinders after the scavenging operation isfinished, means for maintaining the pressure in the low pressurecylinder above atmospheric pressure during the entire expansion movementof the low pressure cylinder.

In testimony whereof we aflix our signatures in presence of twowitnesses.

SVEN GUSTAF WIGELIUS. NILS WVILHELM UHR.

Witnesses GUsTAr SANDBERG, ALFRED ANDERssoN.

